This invention relates to a flow quantity control valve of the type wherein the flow quantity of fluid passing through an orifice is controlled by reciprocating a rod shaped valve member through the orifice located in a fluid passage by utilizing a magnetic attractive force of a solenoid coil.
The flow quantity control valve of this type is used, for example, for controlling the flow quantity of an operating oil supplied from an oil pump of a power steering system of a motor car to a power steering device in accordance with the running speed of the motor car so as to make larger the steering power at the high speed running than that of the low speed running thus giving a steering feeling to the driver adequate for the running speed.
FIG. 1 shows one example of a prior art flow quantity control valve B combined with a power steering oil pump A. A pump housing is constituted by a pair of pump housings 1 and 2 and contains therein such pump constituting parts as a rotor 3 provided with vanes 3a, a cam ring 4, a side plate 5, a pressure plate 6, etc. A drive shaft 7 is journalled by and extends through one housing 1 and its inner end is coupled to the rotor 3. A pulley 8 driven by the engine of the motor car is secured to the outer end of the shaft 7. When the rotor 3 is rotated by the shaft 7, the operating oil supplied to a suction passage 16 from an oil tank, not shown, via a suction pipe 9 is sucked and discharged by vanes 3a of the rotor radially projecting into a pump chamber to be discharged into an output pressure chamber 11 provided on one side of a pressure blade 6. The operating oil in the output pressure chamber 11 is sent to a power steering device, not shown through a discharge passage 12 formed in the housing 2 and an outlet pipe 13, and to a flow control valve 15 via a passage 14 opened in the pressure chamber 11, the flow control valve being provided with a relief valve, so that the output flow quantity of the pump is always maintained at a value less than a predetermined value regardless of the number of revolutions of the engine.
The flow quantity control valve B for controlling the flow quantity of the operating oil in accordance with the running speed of the motor car is combined with the oil pump A in the following manner. More particularly, the flow quantity control valve 8 comprises a cylinder 20 containing a cylindrical plunger 21. One end of the cylinder 20 is fitted into an opening 2a, and it inner end of the cylinder 20 closes an inner passage 2b intercommunicating the output side pressure chamber 11 and the discharge passage 12. An orifice 22 constituting a poppet valve for controlling the flow quantity is formed at the center of the inner end portion. The orifice 22 is communicated with a valve chamber 23 in the cylinder 20, and the valve chamber 23 is communicated with a peripheral annular grooves 25 via axially extending perforations 24, the annular groove 25 being communicated with the output passage 12.
The plunger 21 has a diameter a little smaller than the inner diameter of the cylinder 20. Guide rods 26 and 27 are provided for the opposite ends of the plunger 21 to extend in the axial direction of the plunger 21. The guide rods 26 and 27 are supported by bearings 28 and 29 respectively including balls 28a and 29a to be freely slidable in the axial direction. A rod shaped valve 30 made of nonmagnetic material is provided for one end of one guide rod 26 to move toward and away from the orifice 22 and to project into the valve chamber 23.
The cylinder 20 is constituted by a magnetic cylinder 20a including an extended end provided with the orifice 22, a nonmagnetic ring 20b and a magnetic cylinder 20c following thereto. A solenoid coil 32 wound on a coil bobbin 31 to apply a magnetic attractive force to the plunger 21 is provided about the cylinder 20, thus completing the drive mechanism for the rod shaped valve 30.
Return springs 33 and 34 are provided for the opposite ends of the plunger 21, and the outer end of the cylinder 20 is closed by a plug 35. Covers 36 and 37 are provided to form a magnetic flux passage and to contain the drive mechanism.
In the flow quantity control valve B having a construction described above, where current proportional to the running speed of the motor car is passed through the solenoid coil 32, the plunger 21 would be moved over a distance proportional to the current whereby the rod shape valve 30 would be moved toward and away from the orifice 22 to control the quantity of the pump output. For example, when the car is not running or runs at a low speed no current is supplied to the solenoid coil 32, so that the rod shape valve 30 is sufficiently separated from the orifice 22. Accordingly, the flow quantity supplied to the output passage from the pressure chamber 11 on the output side of the pump via the orifice 22 is not limited so that the all flow quantity is supplied to the power steering device to cause it to manifest its full capability, thus providing smooth steering. On the other hand when the car is running at a high speed, a current proportional thereto is supplied to the solenoid coil 32 to move the plunger 21 and the rod shaped valve 30 to a position closer to the orifice 22 to limit the quantity of the operating oil supplied to the power steering device thus increasing the power to steer the power steering device making it optimum the steering feeling at the time of the high speed running.
As above described, although the flow control valve described above is suitable for the power steering device, it accompanies the following problems. More particularly, a power steering device is included in a pressure oil circuit in which the operating oil circulated through an oil tank, an oil pump, the power steering device and back to the oil tank. The operating oil in the pressure oil tank is contaminated by foreign matters from outside, such impurities and degenerated substances as metal powders produced by the wear of various component parts, circulation of such contaminated operating oil causes damage of various component elements to decrease their life and reliability.
As above described the prior art flow control valve B was constructed such that the bore of the cylinder 20 containing the plunger 30 is communicated with the valve chamber 23 through the orifice 22 so that the impurity, mainly consisting of iron powders would deposit in the magnetic gap and in a small gap between the cylinder 20 and the plunger 21. Consequently, after the use over a long period, the deposited iron powders coagulate to prevent smooth movement of the plunger. In an extreme case, the plunger can not move or the movement thereof would become sluggish. To prevent this problem it is necessary to frequently, inspect, wash and clean and to remove impurities in the operating oil, thus increasing the cost of maintenance.